General anaesthesia causes small areas of lung to collapse (referred to as atelectasis) and many strategies are used to prevent or reverse this, but these strategies only temporarily improve lung function and do not persist into the post anaesthesia care unit (PACU) where atelectasis may still be present. One possible explanation for this is that coughing occurring at the end of the anaesthesic may cause atelectasis to occur. Over 70% of patients cough when their breathing tube is removed as they emerge from the anaesthetic, and our hypothesis is that the presence of the breathing tube prevents a normal cough from occurring and may worsen atelectasis. This study will use alveolar-arterial oxygen difference (AaDO2)as a measure of how well the lungs are oxygenating the blood. This will be measured 30 minutes before the end of the anaesthetic as a control measure of the patient's lung function, and again 60 minutes after the patient has woken up, and the change compared with the amount of coughing observed as the patient emerges from the anaesthetic.